usb: r8a66597-hcd pio to mmio accessor conversion.

r8a66597-hcd is erroneously using PIO routines on MMIO registers, which
presently blows up for any platform that elects to either override or do
away with PIO routines. This managed to work for the common cases since
the PIO routines were simply wrapped to their MMIO counterparts. This
switches over to using the MMIO routines directly, and enables us to kill
off a lot of superfluous casting in the process.

Acked-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>